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78 lines
2.2 KiB
C++
78 lines
2.2 KiB
C++
// Copyright 2022 The Chromium Authors
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "base/cpu_reduction_experiment.h"
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#include <atomic>
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#include "base/check.h"
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#include "base/dcheck_is_on.h"
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#include "base/feature_list.h"
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#include "base/rand_util.h"
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namespace base {
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namespace {
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// Whether to enable a series of optimizations that reduce total CPU
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// utilization.
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BASE_FEATURE(kReduceCpuUtilization,
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"ReduceCpuUtilization2",
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FEATURE_ENABLED_BY_DEFAULT);
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class CpuReductionExperimentSubSampler {
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public:
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CpuReductionExperimentSubSampler() : counter_(base::RandUint64()) {}
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bool ShouldLogHistograms() {
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// Relaxed memory order since there is no dependent memory access.
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uint64_t val = counter_.fetch_add(1, std::memory_order_relaxed);
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return val % 1000 == 0;
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}
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private:
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std::atomic<uint64_t> counter_{0};
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};
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// Singleton instance of CpuReductionExperimentSubSampler. This is only set when
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// the ReduceCpuUtilization experiment is enabled -- as a result, it's ok to
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// assume that the experiment is disabled when this is not set.
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CpuReductionExperimentSubSampler* g_subsampler = nullptr;
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#if DCHECK_IS_ON()
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// Atomic to support concurrent writes from IsRunningCpuReductionExperiment().
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std::atomic_bool g_accessed_subsampler = false;
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#endif
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} // namespace
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bool IsRunningCpuReductionExperiment() {
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#if DCHECK_IS_ON()
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// Relaxed memory order since there is no dependent memory access.
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g_accessed_subsampler.store(true, std::memory_order_relaxed);
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#endif
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return !!g_subsampler;
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}
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void InitializeCpuReductionExperiment() {
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#if DCHECK_IS_ON()
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// TSAN should generate an error if InitializeCpuReductionExperiment() races
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// with IsRunningCpuReductionExperiment().
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//
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// Relaxed memory order since there is no dependent memory access.
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DCHECK(!g_accessed_subsampler.load(std::memory_order_relaxed));
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#endif
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if (FeatureList::IsEnabled(kReduceCpuUtilization)) {
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g_subsampler = new CpuReductionExperimentSubSampler();
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}
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}
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bool ShouldLogHistogramForCpuReductionExperiment() {
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if (!IsRunningCpuReductionExperiment())
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return true;
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return g_subsampler->ShouldLogHistograms();
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}
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} // namespace base
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